1. Field of the Invention
This invention relates to a light emitting diode wafer, alight emitting diode die, and a method of forming light emitting diode dies, more particularly to a method of forming light emitting diode dies including forming die-bonding members over a back surface of a substrate wafer using photolithographic techniques.
2. Description of the Related Art
FIG. 1 illustrates how light emitting diode dies 13 (only one is shown for the sake of brevity) are attached to a package substrate 100 using silver paste 101 (as a die-bonding member) for forming light emitting products, such as lamps or backlight modules. Each of the light emitting diode dies 13 includes a die substrate 11, an epitaxial layered structure 12 formed on the die substrate 11, and a pair of electrodes 131 formed on the epitaxial layered structure 12. Conventionally, the light emitting diode dies 13 are attached to the package substrate 100 through the silver paste 101 using a paste dispensing apparatus. However, the process of attaching the silver paste using the paste dispensing apparatus is relatively time consuming and tedious.
FIGS. 2 and 3 illustrate consecutive steps of a conventional method of forming light emitting diode dies 18, which are ready to be attached to a package substrate (not shown). The method includes the steps of forming an epitaxial layered structure 15 on a substrate wafer 16, forming a layer of an eutectic solder material 17 on a back surface of the substrate wafer 16, and dicing and breaking the substrate wafer 16 along predetermined cutting lines so as to form a plurality of the light emitting diode dies 18, each of which has an eutectic solder layer 19 of the eutectic solder material 17. Ina packaging process, the eutectic solder layers 19 of the light emitting diode dies 18 are pressed against a heated package substrate (not shown) to cause reflow of the eutectic solder layers 19, followed by cooling the eutectic solder layers 19 so as to permit bonding of the light emitting diode dies 18 to the package substrate. A typical example of the eutectic solder material 17 is Gold-Tin (Au—Sn) alloy.
Applicant found that an undesired overflow of a melt of the eutectic solder layer 19 around side walls of each of the light emitting diode dies 18 tends to occur during the reflowing of the eutectic solder layer 19 on the package substrate, which can result in short circuit or current leakage and failure of the light emitting diode dies 18. In addition, since the eutectic solder material 17 is opaque and since alignment marks are formed on a front surface of the substrate wafer 16, alignment of the substrate wafer 16 in a dicing apparatus cannot be conducted using the alignment marks and suitable alignment means other than the alignment marks are required for accurately dicing and breaking the substrate wafer 16 along the predetermined cutting lines.